Microwave tissue resection tool

ABSTRACT

A medical instrument or device is used for resonant delivery of microwave power to tissue for the purpose of resection and coagulation of vessels during surgery and/or other medical procedures. The device enables delivery of large amounts of power to tissue without the need for ground pads by accomplishing an impedance match between tissue and the characteristic impedance of the waveguide that feeds power to it. The device includes a semi-rigid coaxial cable having a center conductor which protrudes from an outer conductor by a length set to be a λ/4 (quarter-wavelength) at the frequency of excitation in the dielectric environment of the tissue of interest. The coaxial cable is shrouded by a dielectric sleeve that provides both thermal and electrical insulation. Fitted against this sleeve is a conductive sleeve whose length is set to be a λ/4 (quarter-wavelength) at the frequency of excitation in the dielectric environment of the dielectric sleeve and the shroud. The device is connected to a feed cable at its proximal end, and can be connected to a source of microwave power. A directional coupler or other wave-sampling mechanism in combination with a power sensor and feedback circuit can be used to monitor reflected power from the device during the procedure, and to control the amount of power supplied to the device.

CLAIM OF PRIORITY

This application is a Continuation-In-Part of co-pending U.S.Non-Provisional Patent Applications entitled “Triaxial Antenna forMicrowave Tissue Ablation” filed Apr. 29, 2004 and assigned U.S.application Ser. No. 10/834,802; “Segmented Catheter for TissueAblation” filed Sep. 28, 2005 and assigned U.S. application Ser. No.11/237,136; “Cannula Cooling and Positioning Device” filed Sep. 28, 2005and assigned U.S. application Ser. No. 11/237,430; “Air-Core MicrowaveAblation Antennas” filed Sep. 28, 2005 and assigned U.S. applicationSer. No. 11/236,985; and “Microwave Surgical Device” filed May 24, 2006and assigned U.S. application Ser. No. 11/440,331; the entiredisclosures of each and all of these applications are hereby hereinincorporated by reference.

This application further claims priority to U.S. Provisional PatentApplications entitled “Segmented Catheter for Tissue Ablation” filed May10, 2005 and assigned U.S. application Ser. No. 60/679,722; “MicrowaveSurgical Device” filed May 24, 2005 and assigned U.S. application Ser.No. 60/684,065; “Microwave Tissue Resection Tool” filed Jun. 14, 2005and assigned U.S. application Ser. No. 60/690,370; “Cannula Cooling andPositioning Device” filed Jul. 25, 2005 and assigned U.S. applicationSer. No. 60/702,393; “Intralumenal Microwave Device” filed Aug. 12, 2005and assigned U.S. application Ser. No. 60/707,797; “Air-Core MicrowaveAblation Antennas” filed Aug. 22, 2005 and assigned U.S. applicationSer. No. 60/710,276; and “Microwave Device for Vascular Ablation” filedAug. 24, 2005 and assigned U.S. application Ser. No. 60/710,815; theentire disclosures of each and all of these applications are herebyherein incorporated by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. Non-Provisional PatentApplications entitled “Triaxial Antenna for Microwave Tissue Ablation”filed Apr. 29, 2004 and assigned U.S. application Ser. No. 10/834,802;“Segmented Catheter for Tissue Ablation” filed Sep. 28, 2005 andassigned U.S. application Ser. No. 11/237,136; “Cannula Cooling andPositioning Device” filed Sep. 28, 2005 and assigned U.S. applicationSer. No. 11/237,430; “Air-Core Microwave Ablation Antennas” filed Sep.28, 2005 and assigned U.S. application Ser. No. 11/236,985; and“Microwave Surgical Device” filed May 24, 2006 and assigned U.S.application Ser. No. 11/440,331; and to U.S. Provisional PatentApplications entitled “Segmented Catheter for Tissue Ablation” filed May10, 2005 and assigned U.S. application Ser. No. 60/679,722; “MicrowaveSurgical Device” filed May 24, 2005 and assigned U.S. application Ser.No. 60/684,065; “Microwave Tissue Resection Tool” filed Jun. 14, 2005and assigned U.S. application Ser. No. 60/690,370; “Cannula Cooling andPositioning Device” filed Jul. 25, 2005 and assigned U.S. applicationSer. No. 60/702,393; “Intralumenal Microwave Device” filed Aug. 12, 2005and assigned U.S. application Ser. No. 60/707,797; “Air-Core MicrowaveAblation Antennas” filed Aug. 22, 2005 and assigned U.S. applicationSer. No. 60/710,276; and “Microwave Device for Vascular Ablation” filedAug. 24, 2005 and assigned U.S. application Ser. No. 60/710,815; theentire disclosures of each and all of these applications are herebyherein incorporated by reference.

FIELD OF INVENTION

The present disclosure relates generally to medical instruments, and inparticular to medical instruments in the field of tissue resection,coagulation, and hemostasis. Specifically, the present disclosurerelates to a medical tool or device for resonant delivery of microwavepower or energy to tissue for the purpose of resection and coagulationof vessels.

BACKGROUND

Use of energy to ablate, resect or otherwise cause necrosis in diseasedtissue has proven beneficial both to human and to animal health.Electrosurgery is a well-established technique to use electrical energyat DC or radio frequencies (i.e. less than 500 kHz) to simultaneouslycut tissue and to coagulate small blood vessels. Radio-frequency (RF)ablation of tumor tissue was developed from the basis of electrosurgery,and has been used with varied success to coagulate blood vessels whilecreating zones of necrosis sufficient to kill tumor tissue withsufficient margin.

Limitations of the above techniques center on the need for ground padson the skin of the patient to provide a return path for the current, aswell as the undesirable stimulation of the nervous system as cuts arebeing made; this usually requires injection of a temporary paralyzingagent. Limitations of tissue impedance, particularly as the tissuebecomes desiccated or charred during the course of the procedure, limitthe amount of current, and hence the amount of ablative power, that canbe applied to the tissue. This in turn limits the size of vessels thatcan be effectively shut down.

Thus current procedures are limited when applied to resection of tumorsfrom highly-vascularized organs, e.g. liver. Furthermore, thelimitations of current and power limit the speed at which theseprocedures can be performed. Accordingly, there is a need for a devicewhich overcomes the problems and disadvantages associated with currentprocedures, and which is an improvement thereover. The presentdisclosure fulfills this need.

SUMMARY

The present disclosure relates to delivery of microwave (e.g.approximately 800 MHz and higher frequencies) power to tissue for thepurpose of ablating tissue or resecting tissue with little or no loss ofblood.

The device enables delivery of large amounts of power (e.g. greater than100 Watts) to tissue without the need for ground pads since itaccomplishes an impedance match between tissue and the characteristicimpedance of the waveguide that feeds power to it. This is accomplishedin a hand-held format similar to many surgical tools. It can accept avariety of tips for different cutting and coagulation purposes.Furthermore, because of the impedance matching, reflected power from thetool is minimized. Reflected power can further be monitored at thegenerator or along the feed cable to use as feedback to the generatorpower control.

Numerous other advantages and features of the disclosure will becomereadily apparent from the following detailed description, from theclaims and from the accompanying drawings in which like numerals areemployed to designate like parts throughout the same.

BRIEF DESCRIPTION OF THE DRAWINGS

A fuller understanding of the foregoing may be had by reference to theaccompanying drawings wherein:

FIG. 1 is a cross-sectional view of a preferred embodiment of thepresent disclosure, showing the arrangement of an impedance-matchingsleeve and the tip.

FIG. 2 is a plan view of the preferred embodiment of the presentdisclosure encapsulated in a ceramic or plastic housing.

FIG. 3 is a schematic circuit diagram for a microwave power delivery andcontrol system in accordance with the preferred embodiment of thepresent disclosure.

DESCRIPTION OF DISCLOSED EMBODIMENT(S)

While the invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will be described herein indetail one or more embodiments of the present disclosure. It should beunderstood, however, that the present disclosure is to be considered anexemplification of the principles of the invention, and theembodiment(s) illustrated is/are not intended to limit the spirit andscope of the invention and/or the claims herein.

With reference to the drawings, an example of the preferred embodimentof the energy delivery device or microwave tissue resection tool of thepresent disclosure is shown in FIG. 1.

As illustrated in FIG. 1, a semi-rigid coaxial cable, preferablyconstructed of copper or silver with a suitable low-loss dielectric,forms the basis of the device. The cable's center conductor 10 protrudesfrom the outer conductor 12 by a length L1, which is set to be a λ/4(quarter-wavelength) at the frequency of excitation (e.g. 915 MHz, 2.45GHz, or another suitable frequency) in the dielectric environment of thetissue of interest. The cable can be chosen from commercially-availablestandards, but it should be thick enough to be rated for the powerdelivered.

The coaxial cable is shrouded by a dielectric sleeve 14 that providesboth thermal and electrical insulation. Fitted against this sleeve is aconductive sleeve (e.g. made of copper or silver or another suitableconductor) whose length is set to be a λ/4 (quarter-wavelength) at thefrequency of excitation (e.g. 915 MHz, 2.45 GHz, or another suitablefrequency) in the dielectric environment of the dielectric sleeve 14 andthe shroud 30 (FIG. 2). This conductive sleeve 16 contacts the outerconductor of the coaxial cable 12 at a point 18, where it is free toslide if necessary to fine-tune the impedance matching effect. It canthen be fixed in place with adhesive or other suitable mechanism.

The protrusion of the coaxial cable's center conductor 10 is shrouded bya non-stick material 20 (e.g. PTFE or Teflon) to minimize adhesion ofthe device to the tissue. A tip 22 at the distal end of the device canbe specially formed to maximize the electric field emanating from it.For example, the tip 22 can be sharpened and optionally exposed directlyto the tissue.

The device is connected to a feed cable at its proximal end 26. Thiscable can be optionally connectorized, by attaching any suitableconnector known in the art of connecting cable, to simplify exchange ofthe device.

As shown in FIG. 2, the device can be enshrouded in a suitable ceramicor plastic housing 30, which can contain cooling fluid (e.g. air,nitrogen, water, etc) and microwave absorbing material (e.g. polyiron)to minimize radiation from the tool to the extent necessary or desired.

As shown in FIG. 3, the device 30 can be used in a system by which it isconnected to a source of microwave power 36 via a cable 32. Adirectional coupler or other wave-sampling mechanism 34 in combinationwith a power sensor and feedback circuit 38 can be used to monitorreflected power from the device during the procedure. If the amount ofreflected power exceeds a threshold, power from the generator 36 can bereduced to minimize heating of the device 30, while if the amount ofreflected power is below a threshold, power can be increased to speedthe procedure.

It is to be understood that the embodiment(s) herein described is/aremerely illustrative of the principles of the present invention. Variousmodifications may be made by those skilled in the art without departingfrom the spirit or scope of the claims which follow.

1. A device for delivery of microwave power to tissue, comprising: acoaxial cable; a resonant sleeve for impedance matching; a resonant tip;and a polymer coating for said tip.
 2. The device of claim 1, furthercomprising a means for controlling the power delivered to the tissuebased on monitoring reflected power from the device.
 3. The device ofclaim 1, wherein the device delivers greater than 100 Watts of power totissue without the need for ground pads.
 4. A medical device comprising:a coaxial cable having a center conductor and an outer conductor; adielectric sleeve shrouding the coaxial cable; and a conductive sleevefitted against the dielectric sleeve and contacting the outer conductor;wherein the center conductor protrudes from the outer conductor by alength, and wherein the device accomplishes an impedance match betweentissue of interest and a characteristic impedance of the waveguide thatfeeds power to the device.
 5. The device of claim 4, wherein theconductive sleeve is positionable to adjust the impedance matchingeffect.
 6. The device of claim 4, wherein the length that the centerconductor protrudes from the outer conductor is set to be aquarter-wavelength at the frequency of excitation in the dielectricenvironment of the tissue.
 7. The device of claim 4, wherein theconductive sleeve has a length set to be a quarter-wavelength at thefrequency of excitation in the dielectric environment of the dielectricsleeve and a shroud which houses the device.
 8. The device of claim 7,wherein the shroud includes cooling fluid.
 9. The device of claim 7,wherein the shroud includes microwave absorbing material.
 10. A methodof delivering microwave power to tissue, comprising the steps of:feeding power to a microwave delivery device; accomplishing an impedancematch between the tissue and a characteristic impedance of the waveguidethat feeds power to the device; and delivering microwave power totissue.